Jumei Zhang

Production of ε-poly-l-lysine by Streptomyces sp. using resin-based, in situ product removal

Resin-based, in situ product removal (ISPR) was used to increase production of ε-poly-l-lysine (PL) by Streptomyces sp. GIM8. D152 resin was selected over Amberlite IRC-50, Amberlite IRC-76 and Amberlite IR-120 to develop ISPR using adsorption capacity and desorption ratio as bases. The yield of PL in response to external PL was unaffected in shake-flask culture; however, the production of PL increased to 2.9 from 0.8xa0gxa0l−1 shake-flasks using ISPR. In a 5xa0l fermentor, 23.4xa0gxa0PLxa0l−1 was achieved compared to 3.76xa0gxa0PLxa0l−1, in the controls by attaching two bags of D152 resin to the probes and baffles of the fermentor.

Prevalence and Characterization of Monophasic Salmonella Serovar 1 ,4,[5],12:i:- of Food Origin in China

Salmonella enterica subsp. enterica serovar 1,4,[5],12:i:- is a monophasic variant of Salmonella Typhimurium, which has recently been recognized as an emerging cause of infection worldwide. This bacterium has also ranked among the four most frequent serovars causing human salmonellosis in China. However, there are no reports on its contamination in Chinese food. Serotyping, polymerase chain reaction, antibiotic resistance, virulotyping, and multilocus sequence typing (MLST) assays were used to investigate the prevalence of this serological variant in food products in China, and to determine phenotypic and genotypic difference of monophasic isolates and Salmonella Typhimurium isolated over the same period. Salmonella 1,4,[5],12:i:- was prevalent in various food sources, including beef, pork, chicken, and pigeon. The study also confirmed the high prevalence (53.8%) of resistance to ampicillin, streptomycin, sulfonamides, and tetracycline in Salmonella 1,4,[5],12:i:-, which was higher than that in Salmonella Typhimurium. Moreover, Salmonella 1,4,[5],12:i:- isolates in our study were different from Salmonella Typhimurium isolates by the absence of three plasmid-borne genes (spvC, pefA, and rck) and the presence of gipA in all isolates. All Salmonella 1,4,[5],12:i:- isolates demonstrated MLST pattern ST34. Genomic deletions within the fljBA operon and surrounding genes were only found in Salmonella 1,4,[5],12:i:- isolates, with all isolates containing a deletion of fljB. However, hin and iroB were identified in all Salmonella 1,4,[5],12:i:- isolates. Three different deletion profiles were observed and two of them were different from the reported Salmonella 1,4,[5],12:i:- clones from Spain, America, and Italy, which provided some new evidence on the independent evolution of the multiple successful monophasic clones from Salmonella Typhimurium ancestors. This study is the first report of Salmonella 1,4,[5],12:i:- in food products from China. The data are more comprehensive and representative, providing valuable information for epidemiological studies, risk management, and public health strategies.

Investigation on the effects of ϵ-poly-L-lysine on a producing strain Streptomyces ahygroscopicus GIM8, for better understanding its biosynthesis

ϵ‐Poly‐L‐lysine (ϵ‐PL) is an L‐lysine homopolymer with strong antimicrobial activity, which is generally produced by Streptomyces strains. ϵ‐PL is only produced under acidic conditions in liquid culture, and to improve the current understanding of ϵ‐PL biosynthesis, the present study was undertaken to investigate the effects of ϵ‐PL on its producer Streptomyces ahygroscopicus GIM8, under acidic and neutral conditions. The results indicated that a neutral pH favored ϵ‐PL adsorption onto the cells, whereas minimal adsorption occurred at pH 4.0, the maximum pH for ϵ‐PL production. At pH 7.0, small amounts of ϵ‐PL caused considerable ATP leakage from the cells, which showed increased membrane permeability. Conversely, ATP leakage was inhibited by ϵ‐PL at pH 4.0. Transmission electron microscopy investigation indicated that the cytoplasmic membrane was the primary site of ϵ‐PL activity at pH 7.0, and that cell shape was maintained. Metabolic activity profiles revealed that ϵ‐PL decreased cellular metabolic activity at a relatively low rate at pH 7.0. However, the toxic effect was significantly enhanced at pH 4.0. Based on these data, a mechanism for the effect of ϵ‐PL on ϵ‐PL‐producing cells under neutral and acidic conditions is proposed. Additionally, acidic conditions may potentially be required for ϵ‐PL biosynthesis in liquid culture because low pH can increase membrane permeability and prevent binding of ϵ‐PL onto cells, both of which favor the secretion of the ϵ‐PL produced by the cells into the broth. This research contributes to the current understanding of ϵ‐PL biosynthesis.

Effects of l-lysine and d-lysine on ɛ-Poly-l-lysine biosynthesis and their metabolites by Streptomyces ahygroscopicus GIM8

Abstractɛ-Poly-l-lysine (ɛ-PL), produced by Streptomyces or Kitasatospora strains, is a homo-poly-amino acid of l-lysine, which is used as a safe food preservative. In this study, the effects of l-lysine and its isomer, d-lysine, on ɛ-PL biosynthesis and their metabolites by the ɛ-PL-producing strain Streptomyces ahygroscopicus GIM8 were determined. The results indicated that l-lysine added into the fermentation medium in the production phase mainly served as a precursor for ɛ-PL biosynthesis during the flask culture phase, leading to greater ɛ-PL production. At an optimum level of 3 mM l-lysine, a ɛ-PL yield of 1.16 g/L was attained, with a 41.4% increment relative to the control of 0.78 g/L. Regarding d-lysine, the production of ɛ-PL increased by increasing its concentrations up to 6 mM in the initial fermentation medium. Interestingly, ɛ-PL production (1.20 g/L) with the addition of 3 mM d-lysine into the initial fermentation medium in flasks was higher than that of the initial addition of 3 mM L-lysine (1.06 g/L). The mechanism by which d-lysine improves ɛ-PL biosynthesis involves its utilization that leads to greater biomass. After S. ahygroscopicus GIM8 was cultivated in the defined medium with L-lysine, several key metabolites, including 5-aminovalerate, pipecolate, and l-2-aminoadipate formed in the cells, whereas only l-2-aminoadipate was observed after d-lysine metabolism. This result indicates that l-lysine and d-lysine undergo different metabolic pathways in the cells. Undoubtedly, the results of this study are expected to aid the understanding of ɛ-PL biosynthesis and serve as reference for the formulation of an alternative approach to improve ɛ-PL productivity using l-lysine as an additional substrate in the fermentation medium.